System for detecting motion, lithographic apparatus and device manufacturing method

Abstract

A system for detecting motion of a body, the system comprising: a body; a first grating mounted substantially stationary relative to a frame of reference; a second grating mounted on the body; a detector arranged to receive one or more radiation beams diffracted at the first and second gratings thereby to detect motion of the body relative to the frame of reference; wherein the detector is coupled to the body and moveable relative to the body.

The invention claimed is; 
     
       1. A system for detecting motion of a body, the system comprising:
 a body comprising a first module and a second module, the first module being moveable relative to the second module; 
 a first grating configured to be stationary relative to a frame of reference; 
 a second grating mounted on the first module; and 
 a detector configured to receive one or more radiation beams diffracted from the first and second gratings to detect motion of the body relative to the frame of reference, 
 wherein the detector is coupled to the body and moveable relative to the body. 
 
     
     
       2. The system of  claim 1 , wherein a body mounted guide is configured to constrain the movement of the detector relative to the body in at least one of the six degrees of freedom excluding in a direction parallel to an elongate direction of the second grating. 
     
     
       3. The system of  claim 1 , wherein a body mounted support is configured to support the detector on the body. 
     
     
       4. The system of  claim 1 , wherein a bearing is configured to couple the body to the detector are coupled by a bearing. 
     
     
       5. The system of  claim 1 , further comprising a grating guide configured to:
 be stationary relative to the first grating; and 
 constrain movement of the detector relative to the first grating in at least one of the six degrees of freedom excluding in a direction parallel to an elongate direction of the first grating. 
 
     
     
       6. The system of  claim 1 , further comprising a detector actuator configured to move the detector relative to the body in a direction parallel to an elongate direction of the second grating. 
     
     
       7. The system of  claim 6 , wherein the detector actuator is configured to generate a force between the body and the detector. 
     
     
       8. The system of  claim 6 , wherein the detector actuator is configured to generate a force between a third body and the detector. 
     
     
       9. The system of  claim 1 , wherein the detector is moveable relative to the body by passive action of a guide. 
     
     
       10. The system of  claim 1 , wherein, in use, the detector is under the first and second gratings and the second grating is under the first grating. 
     
     
       11. A system for detecting motion of a body, the system comprising:
 a body; 
 a first grating configured to be stationary relative to a frame of reference; 
 a second grating mounted on the body; 
 a detector configured to receive one or more radiation beams diffracted from the first and second gratings to detect motion of the body relative to the frame of reference; 
 a guide configured to guide the detector in a direction parallel to an elongate direction of the first grating; and 
 an actuator configured to move the detector in a direction parallel to the elongate direction of the first grating. 
 
     
     
       12. The system of  claim 11 , further comprising a third grating configured to be stationary relative to the frame of reference and parallel to the first grating. 
     
     
       13. The system of  claim 12 , further comprising another detector configured to receive one or more radiation beams diffracted from the third grating and second grating to detect motion of the body relative to the frame of reference. 
     
     
       14. The system of  claim 12 , wherein the first grating and the third grating are part of the same object. 
     
     
       15. The system of  claim 11 , further comprising a fourth grating mounted along a first edge of the body, the first edge being opposite to a second edge of the body on which the second grating is mounted. 
     
     
       16. A lithographic apparatus comprising;
 a support configured to hold a patterning device, the patterning device being capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam; 
 a projection system configured to project the patterned radiation beam onto a target portion of a substrate; 
 a frame of reference configured to be stationary relative to the projection system; 
 a body comprising a first module and a second module, the first module being moveable relative to the second module; 
 a first grating configured to be stationary relative to the frame of reference; 
 a second grating mounted on the first module; and 
 a detector arranged to receive one or more radiation beams diffracted at the first and second gratings to detect motion of the body relative to the frame of reference, 
 wherein the detector is coupled to the body and moveable relative to the body. 
 
     
     
       17. The lithographic apparatus of  claim 16 , wherein the body is a substrate stage for supporting a substrate.